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Natural channel design (NCD) and analytical channel design (ACD) are two competing approaches to stable channel design that share fundamental similarities in accounting for sediment transport processes with designs based on hybrid fluvial geomorphology and hydraulic engineering methods. In this paper, we highlight the linkage between ACD's capacity/supply ratio (CSR) and NCD's sediment capacity models (FLOWSED/POWERSED), illustrating how ACD and NCD have reached a point of convergent evolution within the stream restoration toolbox. We modified an existing CSR analytical spreadsheet tool which enabled us to predict relative channel stability using both conventional bed load transport equations and regional sediment regression curves. The stable channel design solutions based on measured data most closely matched the Parker (ACD) and/or Pagosa good/fair (NCD) relationships, which also showed the greatest CSR sensitivity in response to channel alterations. We found that CSR differences among the transport relationships became more extreme the further the design width deviated from the supply reach, suggesting that a stable upstream supply reach may serve as the best design analog. With this paper, we take a step toward resolving lingering controversy in the field of stream restoration, advancing the science and practice by reconciling key differences between ACD and NCD in the context of reach scale morphodynamics. [ABSTRACT FROM AUTHOR]

Past geomorphological models assume that erosion of sediments from old mountain belts occurred at a relatively constant rate, based on comparatively uniform isostatic adjustment caused by unloading. Late Miocene strata of the south-eastern United States provide an example of pulsed tectonism resulting in a surge in siliciclastic sediment production and transport. Regional tectonism (uplift of the southern Appalachian Mountains) and climatic conditions during the Late Miocene resulted in the long-distance (up to 1000 km) fluvial transport of coarse siliciclastic sediments onto a stable carbonate platform in southern Florida. The sediments are unusual in that they are significantly coarser than marine-transported sands in southern Florida, with discoidal quartz and quartzite clasts up to 40 mm in diameter locally present, and have relatively high potassium feldspar contents (up to 16% in some sample fractions), whereas feldspar is rare in modern Florida beach sands. It is suggested that previously documented rejuvenation of the southern Appalachian Mountains during the Middle to Late Miocene time, coupled with the Messenian sea-level low, generated the increased rate of sediment production and necessary hydraulic gradient to allow rapid transport of coarse sediments. Tectonic influence on the river pathway in Florida, as well as in the southern Appalachian Mountains, may have maintained the river on the narrow carbonate platform. The Florida Platform during the Late Miocene must also have had a sufficiently wet climate to cause episodic transport of the coarse sediments. Siliciclastic sediment transport on the Florida Platform during the Late Miocene greatly differed from Pleistocene to modern conditions, which are dominated by the transport of fine-grained sands by longshore marine processes. [ABSTRACT FROM AUTHOR]

Despite geomorphic processes being increasingly recognized as a vital component of river management projects, evidence suggests that they may not be adequately captured in common river assessment procedures. We reviewed 91 river assessment procedures from around the world to evaluate their effectiveness in capturing geomorphic processes relevant for river management goals. Our objectives were to summarize which common geomorphic indicators are measured and how in different types of river assessments categorized based on their main focus: geomorphic, physical habitat, mixed geomorphic and habitat, and hydromorphology. Our analysis identified differences in the types of geomorphic indicators included and measurement methodologies between the types of assessment procedures. Some geomorphic processes, such as sediment transport, are nearly completely absent from all assessments, despite their importance for geomorphic processes. The variability among assessment procedures suggests that a single procedure is unlikely to capture all geomorphic components required to support every river management programs. Here, we discuss how the strengths and limitations of different assessment types can be used to guide decisions around how to select assessments and geomorphic indicators to support management project goals. A companion paper expands the discussion of how to plan effective river assessment procedures to support unique management goals. [ABSTRACT FROM AUTHOR]

In mountain environments, steep slopes and intense precipitation favour high rates of soil erosion and sediment delivery into rivers, which can cause major problems, such as agricultural soil loss, decreased water quality and excessive sedimentation. The understanding of cause-effect relationships between rainfall, runoff, sediment production and transport is therefore of primary importance to improve our ability to predict spatially-distributed erosion rates and sediment yields at the basin outlet.When measuring suspended sediment concentrations at the outlet of a river basin, a large variability is usually observed in the rating curve, i.e. the suspended sediment concentration (SSC) as a function of discharge (Q). The source of this scatter is generally attributed to the inherent stochasticity of the sediment production and transport processes involved along the sediment pathways in a catchment. In this study, we show that scatter in the SSC-Q relationship may also arise in fully deterministic modelling of catchment sediment production and transport by overland flow. For this purpose, we developed a hillslope and channel suspended sediment flow component in the spatially distributed hydrological model TOPKAPI-ETH. By applying the model to the Kleine Emme watershed (Switzerland), we explore how variability in the SSC-Q rating curve is affected by (a) rainfall variability in space, (b) surface erodibility distribution in space and (c) spatial connectivity of sediment sources to the channel network. We complement the analysis by investigating the sediment delivery ratios (SDRs) as a measure of the connectivity of the sediment sources to the channel network. We show that the variability in rainfall contributes to the scatter in the SSC-Q relation, because it activates localized sources of sediment production. Based on the model assumption that sediment discharge equals the transport capacity of overland flow, spatially variable surface erodibility introduces areas of localized increased sediment productivity and others of low transport capacity where sediment may be deposited. Overall, this results in a reduction of SSC variability at the outlet, due to a decreased sediment connectivity at the catchment scale. The SDR analysis supports this result, by showing a significantly lower sediment connectivity when spatially variable surface erodibility is considered, i.e. when the presence of sediment buffers is simulated. The analysis also shows that sediment connectivity increases in the downstream direction due to the absence of significant sediment sinks in the catchment. The upper part of the basin has a lower sediment connectivity than the tributaries, due to a Last Glacial Maximum landscape disconnected from the fluvial network. To summarize, we conclude that (1) spatially-distributed deterministic models of rainfall-runoff-erosion processes can generate large variability in SSC for a given discharge; (2) the spatial distribution of rainfall and the connectivity of localized sediment sources to the channel network are key to capture the scatter in the SSC-Q relation. Furthermore, our results show that the connectivity of sediment transport can vary significantly within a catchment with a diverse geomorphology and the location of buffers of sediment transport on hillslopes plays an important role in determining the global sediment connectivity. [ABSTRACT FROM AUTHOR]

The activity of fallout radionuclides (7Be, 137Cs, and 210Pb) was measured on upland and floodplain soils and on suspended sediments to quantify sources of fine sediment and to estimate sediment transport distances in stream channels in the Yellowstone River basin. Samples were collected seven times during snowmelt and runoff at nine locations from the headwaters of Soda Butte Creek to Billings, Montana, a 423-km-long reach of channel. The inventory of radionuclides in soil increases with precipitation and is highest in the headwaters. The activity of radionuclides in suspended sediment decreases downstream, and more activity is observed earlier than later in the flood hydrograph. The radionuclide activity of sediment derived from erosion of upland soils differs from that derived from bank erosion. Fine suspended sediment has an intermediate radionuclide signature that is quantified in terms of the relative contribution of these two sources of fine sediment. At sites high in the drainage, soils contribute 50% to the suspended load and this value decreases to 11%–26% downstream. Fine sediment transport distances were calculated from the exponential decrease in radionuclide concentration below a point source. Transport distances increase from a few kilometers in the headwaters to hundreds of kilometers downstream. These estimates are consistent with transport distances estimated from the settling velocity of the particles and from the distribution of mine tailings downstream from a dam failure. This study of a large watershed confirms earlier results from smaller basins and suggests that transport distances increase with basin size. [ABSTRACT FROM AUTHOR]

The Atchafalaya River in south-central Louisiana is of geomorphic interest because of the large volumes of flow and sediment transported and its role as a major floodway for the lower Mississippi River, notwithstanding its potential to become an avulsion pathway at Old River. Since its origin in the sixteenth century, it has undergone many transformations and currently receives flow from the Red River and partial flow of the Mississippi River through multiple pathways. Flow increased progressively beginning in the mid-1800s and continued until concerns of diversion spurred placement of engineering structures to regulate flows at the juncture between the Mississippi and Atchafalaya rivers in 1963. Prior studies, that looked at reaches or six to seven rangelines or cross sections on hydrographic surveys document areal, width, and depth increases in the uppermost 80 km (50 mi) of the Atchafalaya River from 1880 to 1974. This study assesses how channel geometry of the Atchafalaya River has changed with flow variations since the 1880s by evaluating instantaneous discharge measurements that document change at superior temporal resolution and differences in thalweg values from coupled modern hydrographic surveys which document change at better spatial resolution than prior works. While structures have regulated and limited flow into the Atchafalaya since 1963, the highest values of discharge, cross-sectional area, and width at Simmesport (upstream) follow river regulation. Associated geometry data at Simmesport and Morgan City (downstream) document that mean bed and thalweg elevations have risen. Comparison of thalweg elevations on hydrographic surveys from 1963 and 2006 show pronounced local variability in bed elevation change but also reaches dominated by degradation (including the Red River and uppermost section of the Atchafalaya) near the Old River diversion. Aggradation occurs in the lower Atchafalaya, a zone where along-channel lakes are filling, flow and sediment quantities are changing in part caused by the constructed Wax Lake Outlet, and deltas have been growing in Atchafalaya Bay. Findings are relevant to river engineering and flood management, especially navigation, and help in better understanding the evolution of large distributaries and the role of human impacts. [ABSTRACT FROM AUTHOR]

Abstract: Radar-revealed palaeodrainage systems are analyzed using Radarsat-1 data covering the Kufra Oasis and parts of southeastern Libya and northern Chad. The analysis shows that two mega fluvial systems exist to the south of the Kufra Oasis. Along the western one, a mappable polygonal fluvial unit covers 13,628km2 in area, with the entire watershed extending north beyond the borders of the present 347,160km2 study area. The eastern system covers 4321km2 in area and is morphologically similar to the Amazon’s Rio Negro, although the African channel is four times wider. The enormity of these features provides some explanation as to why continuous extraction of groundwater in the oasis and nearby circular irrigation farms is possible. Clearly, these mega fluvial systems formed at some time in the past when rain was plentiful over a protracted time period. [Copyright &y& Elsevier]

This study aimed to characterize the sedimentary facies and understand the morphodynamics of the study area, and their results were correlated with various analytical methods. Different analyses such as depositional environmental, statistical, shoreline change, and grain size illustrated the temporal and spatial distribution of sediments. It has previously been claimed that current research locations are locii to fluvial landforms and are affected by fluvial processes. However, there are currently no rivers in the study region. This study was done to better understand the presence of fluvial landforms and to evaluate the previous findings. The dynamic behavior of the coast was revealed through shoreline analysis, which was done using satellite images from various years. Oceanographic parameters and longshore sediment transport play a vital role in geomorphological changes in coastal zones. According to the grain size analysis results, mean values showed that the deposits predominantlyare medium grained. The outcome discussed the spatiotemporal variations in geomorphology, sedimentation, and the function of coastal and fluvial processes on the beach of an island and a sand spit. Also highlighted was the role that wave action, fluvial currents, and tidal currents had in the long-term evolution of coastal geomorphological features such as spits, beaches, open coasts, and islands. The standard deviation signifies that the sediments are very well sorted to poorly sorted. Skewness ranges from fine skewed to strongly fine skewed and the kurtosis values show that the sediments are predominately very platykurtic which implies a low-energy environment of deposition. Four sedimentary facies (Facies A, B, C, D) have been found and facies A, B, and C may be wave-influenced deposits, but facies D may be formed by fluvial processes and contain medium to sand-sized particles. The direction of the tip area is also pointing to the south and this result concluded that the tip area is continuously growing. Thus, the results of this study revealed that sediment transport and coastal geomorphology evolution may be governed by two main processes such as the present ocean hydrodynamics and paleo fluvial processes of the study regions. [ABSTRACT FROM AUTHOR]

This work presents FLUNETS (FLUvial NETwork Sorting tool), a new MATLAB-based tool designed for channel network ordering by Horton and Hack hierarchies. Differently to Strahler and Shreve hierarchies, Hack and Horton orderings allow organizing a drainage network in a hierarchy, identifying the parent segment over the child segment, giving as a result a network where the value of a river remains unchanged from the mouth upstream to the headwater. The novelty of FLUNETS is that it allows the user to choose the hierarchy attribute. Therefore, a fluvial network can be ordered by distance to the mouth or by accumulation upstream. In addition, FLUNETS offers a wide set of optional parameters, which turns it into a friendly tool to attain a highly tailored ordered fluvial network. A continuous fluvial network is the starting point for multiple landscape analysis applications. The source code is available in the authors' GitHub account (https://github.com/geouned/FLUNETS). [ABSTRACT FROM AUTHOR]

Complex relationships between stream functions and processes make evaluation of stream modification projects difficult. Informed by vague objectives and minimal monitoring data, post-construction project evaluations can often be a subjective attribution of success or failure. This article provides a simple framework to rapidly describe the degree of damage in stream modification projects performed in constrained settings. Based on widely accepted evaluations of physical habitat quality and stream stability, the damage states framework describes a continuum of damage in multiple categories that relate natural stream functions to the often desired state of static equilibrium. Given that channel form is closely related to stream function, it follows that changes to the channel form result in changes in function. The damage states focus on damage to flow hydraulics, sediment transport and channel equilibrium, hydraulic, and geomorphic parameters that describe basic stream functioning and support higher level functions in the modified channel. The damage states can be used in decision making as a systematic method to determine the need for repair and design adjustments. [ABSTRACT FROM AUTHOR]

This progress report on the discipline of fluvial geomorphology reviews 134 papers, 112 of which were published in Earth Surface Processes and Landforms (ESPL) during the calendar years of 2008 and 2009. It continues where the last report for 2006 and 2007 (Stott, 2010) ended. Papers are again grouped by themes to cover 10 subdisciplines within the subject area. The themes were chosen by classifying all geomorphological articles published in ESPL for the same period, of which 38% were within the subject area of fluvial geomorphology. Themes (in order of number contributing to the total) were: fluvial sediment transport; soil erosion and control; modelling the fluvial environment; river management, restoration and effects of vegetation on fluvial systems; gully and hillslope sediment transfer; river regulation, channel change and human influences; advances in methodology in fluvial geomorphology; fluvial hydraulics; fluvial chronology; and bank erosion in fluvial systems. The 2006–2007 and 2008–2009 periods are compared and it was found that broadly the same themes retained their popularity (in terms of numbers of papers published) as in the previous report for 2006–2007. [ABSTRACT FROM AUTHOR]

• Overlapping crater populations constrain the total era of martian valley formation. • Martian valleys may have formed intermittently over hundreds of millions of years. • Long-term erosion rates would have been similar to the modern Atacama Desert. A number of studies have constrained the cessation of martian valley network activity to around the Noachian-Hesperian boundary, but the total time period over which these features formed remains poorly constrained. Most attempts to ascertain valley network formative timescales rely on an intermittency factor that varies widely for terrestrial rivers and is unknown for Mars. In this contribution, superposition relationships are used to identify crater populations that pre- and postdate valley network incision, resulting in maximum cumulative valley formation times of ∼108 years. These timescales correspond with long-term erosion rates of ∼0.25 m/Myr, similar to those calculated for the Middle to Late Noachian as well as the central Atacama Desert since the Late Miocene. Assuming sediment transport rates previously calculated for other martian valley networks, this implies a minimum fluvial intermittency of ∼10−5, several orders of magnitude lower than modern day Earth rivers but similar to values independently calculated for some martian fluvial deposits. This low intermittency suggests that martian valley incision may have been significantly hindered by erosion into existing bedrock or by boulder armoring of the valley floor. Alternatively, unlike river valleys on Earth, runoff events driving martian valley network activity may have been non-seasonal, Milankovitch-like cycles, with long eras of quiescence between periods of intensified fluvial activity. [ABSTRACT FROM AUTHOR]

1. Rivers are subject to thresholds of several types that define significant changes in processes and morphology and delimit distinctive riverine landscapes and habitats. Thresholds are set by the conditions that govern river channel process and form, amongst which the most important are the flow regime, the quantity and calibre of sediment delivered to the channel, and the topographic setting (which determines the gradient of the channel). These factors determine the sediment transport regime and the character of alluvial deposits along the channel. 2. Changes occur systematically along the drainage system as flow, gradient and sediment character change, so a characteristic sequence of morphological and habitat types – hence of riverine landscapes – can be described from uplands to distal channels. The sequence is closely associated with stream competence to move sediment and with bank stability. 3. The paper proposes a first order classification of river channel and landscape types based on these factors. The riverine landscape is affected seasonally by flow thresholds, and further seasonal thresholds in northern rivers are conditioned by the ice regime. 4. It is important to understand geomorphic thresholds in rivers not only for the way they determine morphology and habitat, but because human activity can precipitate threshold crossings which change these features significantly, through either planned or inadvertent actions. Hence, human actions frequently dictate the character of the riverine landscape. [ABSTRACT FROM AUTHOR]

Amplified warming of high latitudes and rapid thaw of frozen ground threaten permafrost carbon stocks. The presence of permafrost modulates water infiltration and flow, as well as sediment transport, on soil-mantled slopes, influencing the balance of advective fluvial processes to diffusive processes on hillslopes in ways that are different from temperate settings. These processes that shape permafrost landscapes also impact the carbon stored on soil-mantled hillslopes via temperature, saturation, and slope stability such that carbon stocks and landscape morphometry should be closely linked. We studied >69,000 headwater basins between 25° and 90 °N to determine whether the thermal state of the soil sets the balance between hillslope (diffusive) and fluvial (advective) erosion processes, as evidenced by the density of the channel networks (i.e., drainage density) and the proportion of convex to concave topography (hillslopes and river valleys, respectively). Watersheds within permafrost regions have lower drainage densities than regions without permafrost, regardless of watershed glacial history, mean annual precipitation, and relief. We find evidence that advective fluvial processes are inhibited in permafrost landscapes compared to their temperate counterparts. Frozen soils likely inhibit channel development, and we predict that climate warming will lower incision thresholds to promote growth of the channel network in permafrost landscapes. By demonstrating how the balance of advective versus diffusive processes might shift with future warming, we gain insight into the mechanisms that shift these landscapes from sequestering to exporting carbon. [ABSTRACT FROM AUTHOR]

Changes in 137Cs export over time following clearcutting were investigated in a Japanese forested catchment affected by the Fukushima nuclear accident. A total of 13% of the catchment area was clear-cut 2 years after the accident. Annual suspended solids (SS) export at the catchment outlet increased 1.4 to 2.0 times after clearcutting; however, 137Cs export increased slightly (up to 1.1 times), corresponding to 0.21% to 0.30% of the 137Cs inventory in the catchment. The smaller change in 137Cs export than in SS export was due to a rapid decrease in the activity concentration following clearcutting. This decrease was likely caused by both natural attenuation and SS derived from sources with a low activity concentration in the clear-cut area. Monitoring of the sediment transport from hillslopes in small-scale experimental plots showed that the 137Cs yield in the skid trail was 3.6 to 21 times greater than those in clear-cut and unlogged forest floors. This significant 137Cs transport was due to greater soil erosion (by up to two orders of magnitude) along the skid trail, despite the lower activity concentration than those in the other plots. This indicates that while skid trails were involved in the rapid decrease of the activity concentration of SS, they were a potential source of the increased export of 137Cs and SS. Net 137Cs export increased by clearcutting (the export excluding the decrease accompanied by natural attenuation) was estimated to account for only 0.092% of the inventory in the catchment for 2.5 years. These results imply that the impact of clearcutting on 137Cs export was temporary in this catchment. [ABSTRACT FROM AUTHOR]

Uranium (U) isotopes can be used to estimate the comminution age of sediments , i.e. the time elapsed from sediment production on continents, via weathering and physical erosion, to deposition in the sedimentary record. The calculation of this comminution age is based on measured (234U/238U) activity ratios in river sediments, and inferred time-dependent recoil effect, which leads to the preferential release of 234U from mineral lattices during erosion processes. In this study, we report on a large-scale (234U/238U) investigation of modern river sediments worldwide, with the aim to determine the extent to which parameters such as grain size, lithology, weathering, climate and geomorphology may influence the distribution of U isotopes in fine-grained sediments. Our extensive dataset (N = 64) includes U isotopic measurements for many of the world's largest rivers, but also rivers draining particular climatic and geological settings. Our results indicate that sediments collected from river basins draining mostly igneous, metamorphic or volcanic rocks often display (234U/238U) ratios > 1, with clay-size fractions (<4 µm) being less depleted in 234U (higher 234U/238U) than corresponding silt-size fractions (4–63 µm). In contrast, sediments derived from multi-lithological basins or draining sedimentary rocks are typically characterized by (234U/238U) ratios <1, with clays generally exhibiting more depleted 234U signatures than silts. Taken together, these observations suggest that the formation of secondary clay minerals in soils from basins draining mostly igneous, metamorphic is accompanied by partial incorporation by recoil injection of 234U initially released during weathering processes, possibly from U-rich minerals, such as sphene or apatite. Instead, in multi-lithological catchments draining sedimentary rocks, we propose that the erosion of recycled sediments having experienced several cycles of weathering, possibly over glacial-interglacial timescales, could explain the much lower (234U/238U) ratios observed in clay-size fractions. While no direct relationships can be identified between sediment (234U/238U) ratios and lithology, weathering intensity, climatic or geomorphic parameters in corresponding river basins, we show that the catchment size probably plays an important role in controlling the distribution of (234U/238U) in river sediments, through its direct influence on the sediment residence time. Finally, a multiple regression analysis of our data, combining various environmental parameters for the lithology, climate and geomorphology of studied river basins, indicates predicted (234U/238U) values that are very similar to measured values (with R2 ∼ 0.8). This finding provides further support for the usefulness of (234U/238U) ratios in the sedimentary record for reconstructing past landscape changes and their effect on sediment transport and residence time in river basins. [ABSTRACT FROM AUTHOR]

Abstract: This paper uses a multifaceted remote sensing and morphometric approach to investigate if the surface of subcatchments in the Parana Valles area of Mars (20–30°S, 0–20°W) is reflective of hydrology and sediment transport by water. Using digital elevation model (DEM) data obtained from the Mars Orbiter Laser Altimeter (MOLA), three nested subcatchments were examined using a suite of terrestrial geomorphic and hydrologic statistics to determine if their shape and form lies within the known range of fluvial catchment properties on Earth. Further, an examination of statistical accuracy via an innovative pixel-by-pixel solution of two statistics established that despite mineralogical homogeneity confirmed by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral survey, erosion processes were likely to be variable across the study site. The DEM-based methods outlined here can be employed at other sites to investigate geomorphic properties and attributes of the Martian surface. [Copyright &y& Elsevier]

In the Latnjavagge drainage basin (68°21'N, 18°29'E), an arctic-oceanic periglacial environment in northernmost Swedish Lapland, the fluvial sediment transport and the characteristics and importance of high-magnitude/Iow-frequency fluvial events generated by intense snowmelt or heavy rainfall have been investigated and compared with snowmelt- and rainfall-induced discharge peaks in the Levinson-Lessing Lake basin (Krasnaya river system) on the Tairnyr Peninsula, an arctic periglacial environment in northern Siberia (74°32'N, 98°35'E). In Latnjavagge (9 km²) the intensity of fluvial sediment transport is very Iow. Most of the total annual sediment load is transported in a few days during snowmelt generated runoff peaks. Due to the continuous and very stable vegetation covering most areas below 1300 m a.s.l. in the Latnjavagge catchment, larger rainfall events are of limited importance for sediment transport in this environment. Compared to that, in the c. 40 times larger Krasnaya river system rainfall-generated runoff peaks cause significant sediment transport. The main sediment sources in the Latnjavagge drainage basin are permanent ice patches, channel debris pavements mobilized during peak discharges and exposing fines, and material mobilized by slushflows. In the Krasnaya river system river bank erosion is the main sediment source. In both periglacial environments more than 90% of the annual sediment yield is transported during runoff peaks. The results from both arctic periglacial environments underline the high importance of high-magnitude/ Iow-frequency fluvial events for the total fluvial sediment budgets of periglacial fluvial systems. Restricted sediment availability is in both arctic environments the major controlling factor for this behaviour. [ABSTRACT FROM AUTHOR]

We review the role of science in shaping river flood risk management policy in England, highlighting the relatively recent influence of fluvial geomorphology, river ecology, climate change and ecosystem services in evidence-based decision-making. These disciplines, together with an historical perspective, catchment-scale delivery, integrated land and water management planning, and adaptive management are crucial in managing future flood risk. A central tenet of previous land drainage policy was a professional (and public) mindset about flood 'prevention' solutions for river flooding. As a direct consequence, more than 8,500 km of rivers were 'improved' by mechanical dredging during the 1930s to 1980s; habitats were destroyed, but flooding continued. A more enlightened, long-term approach has since evolved in response to environmental imperatives and lessons learnt from several major floods during the last two 'flood-rich' decades. River science, local knowledge and land management incentives allow more natural processes to be restored in river catchments. The natural capital and ecosystem service benefits of river systems are now better understood and quantified, whereas the importance of sediment transport is fully recognised, with sources and sinks treated more holistically than in the past. Evaluating the outcomes of innovative runoff and river management techniques from both physical and socioeconomic perspectives will determine the success of a catchment-based approach. We highlight some of the uncertainties, nuances and assumptions associated with recent initiatives such as Natural Flood Management, Citizen Science and Flood Action Groups. Further integration between policy, strategic planning and local delivery is needed to anticipate and respond to climate and catchment land use changes. River science will play a crucial part in identifying the most effective way of improving flood management and in a way that helps to deliver the recovery of nature. It will inform adaptive management to cope with climate change. [ABSTRACT FROM AUTHOR]

• An efficient 2D shallow water hydro-sediment-morphodynamic model is presented. • Morphodynamic processes under the impact of cascade movable weirs are studied. • Disparate morphological changes may result under different operation schemes. • An alternating operation scheme is proposed to constrain morphological changes. Cascade movable weirs have been increasingly widely used for river landscaping, water storage and ecological wellbeing. The weirs disturb the prior equilibrium in line with fluvial hydrology, sediment transport and geomorphology, and may lead to profound changes in the river, of which, however, the understanding has so far remained poor. Here, the first of its kind, a computational modelling study is presented on the morphodynamic processes under the impact of cascade hydraulic lifting dams, a type of movable weirs, as to the middle Fen River, China. A two-dimensional shallow water hydro-sediment-morphodynamic model is applied to resolve the fluvial processes, which is physically coupled and computationally efficient based on Finite Volume Method, unstructured mesh, local time stepping and parallel computing. Computational results show that the cascade dams alter the flow and sediment transport locally and on the reach scale in a distinct manner under different operation schemes, which in turn incur disparate morphological changes. Collapse of all the dams all year round would lead to net degradation in the study reach, with the floodplains aggrading and the main channel degrading. Operation of all the dams all year round may induce an overall aggradation both on the floodplains and in the main channel. If all the dams collapse in flood seasons and operate in dry seasons (CF), degradation occurs in the main channel whereas the floodplains experience aggradation, with a net degradation. When only the dams in the main channel operate all year round (OM), the floodplains degrade while the main channel aggrades, resulting in a net aggradation in the study reach. Either aggradation or degradation may prevail locally on floodplains, in main channel and individual subreaches. The present findings lead us to propose a complex operation scheme of annually alternating CF and OM to constrain significant morphological changes. [ABSTRACT FROM AUTHOR]

A landscape's sediment grain size distribution is the product of, and an important influence on, earth surface processes and landscape evolution. Grains can be large enough that the motion of a single grain, infrequently mobile in size-selective transport systems, constitutes or triggers significant geomorphic change. We define these grains as boulders. Boulders affect landscape evolution; their dynamics and effects on landscape form have been the focus of substantial recent community effort. We review progress on five key questions related to how boulders influence the evolution of unglaciated, eroding landscapes: 1) What factors control boulder production on eroding hillslopes and the subsequent downslope evolution of the boulder size distribution? 2) How do boulders influence hillslope processes and long-term hillslope evolution? 3) How do boulders influence fluvial processes and river channel shape? 4) How do boulder-mantled channels and hillslopes interact to set the long-term form and evolution of boulder-influenced landscapes? 5) How do boulders contribute to geomorphic hazards, and how might improved understanding of boulder dynamics be used for geohazard mitigation? Boulders are produced on eroding hillslopes by landsliding, rockfall, and/or exhumation through the critical zone. On hillslopes dominated by local sediment transport, boulders affect hillslope soil production and transport processes such that the downslope boulder size distribution sets the form of steady-state hillslopes. Hillslopes dominated by nonlocal sediment transport are less likely to exhibit boulder controls on hillslope morphology as boulders are rapidly transported to the hillslope toe. Downslope transport delivers boulders to eroding rivers where the boulders act as large roughness elements that change flow hydraulics and the efficiency of erosion and sediment transport. Over longer timescales, river channels adjust their geometry to accommodate the boulders supplied from adjacent hillslopes such that rivers can erode at the baselevel fall rate given their boulder size distribution. The delivery of boulders from hillslopes to channels, paired with the channel response to boulder delivery, drives channel-hillslope feedbacks that affect the transient evolution and steady-state form of boulder-influenced landscapes. At the event scale, boulder dynamics in eroding landscapes represent a component of geomorphic hazards that can be mitigated with an improved understanding of the rates and processes associated with boulder production and mobility. Opportunities for future work primarily entail field-focused data collection across gradients in landscape boundary conditions (tectonics, climate, and lithology) with the goal of understanding boulder dynamics as one component of landscape self-organization. • We synthesize work to date exploring how boulders affect the evolution of nonglaciated, eroding hillslopes and channels. • Boulder dynamics are one facet of landscape self-organization, influencingtransient adjustment and steady-state form. • The effects of boulders on landscape shape can be quantified by combining field data with simplified theoretical models. • The key research need is for more field data on boulder dynamics spanning gradients in boundary conditions. [ABSTRACT FROM AUTHOR]

Abstract: Riverine assessments of channel morphology and fluvial processes typically involve a time-consuming survey of channel cross sections and longitudinal profiles, expensive aerial imagery, and/or require specialised knowledge. As a result, geomorphic input is not widely included in multiparameter river condition assessments. We were interested in determining if surface flow type observations can be used as a rapid measure of channel morphology and then subsequently be used in river condition assessments to monitor channel change over time. We examined the relationship between flow types (e.g., rippled flow, no perceptible flow) and channel morphology. Two aspects of channel morphology were assessed: (i) within-reach depth variability and (ii) cross section geometry (e.g., width, area, Froude number). In a two-part study, each of these was correlated with flow type diversity for a range of study sites from upland and lowland environments in Victoria, Australia. We found that an increased diversity of flow types correlated with greater depth diversity, based on the coefficient of variation of depth along a reach. Flow types also correlated well with the cross-sectional Froude number, but less so with other geometric parameters. The proportion of flow types present was also notably sensitive to discharge within the low flow range examined (70–99% flow exceedance). Three ‘geo-topes’ — cross section units of a dominant flow type — were found to be the most physically distinct units at this cross section scale; no perceptible flow (deadwater), smooth boundary turbulent (glide), and rippled flow (run/riffle). Rippled flow is a revision to previous run/riffle classifications and is identified by the presence of unbroken waves of any size with crests moving in a general downstream direction. Our findings indicate that flow types can provide indicative information on channel morphology along a reach. When assessed at low flow levels, the diversity of flow types reflects the variability of cross-sectional geometry and also the diversity of the channel bed (depth). On this basis, the inclusion of flow type observations in river condition assessments can provide meaningful information on channel morphology, in a rapid and repeatable way. With repeat surveys, flow types could be used as a geomorphic metric to track changes in morphologic diversity over time, including changes associated with processes of sediment transport, scour, and deposition at a reach. [Copyright &y& Elsevier]

Bank erosion frequently occurs in the Lower Yellow River (LYR), playing an important role in the evolution of this braided river. A two-dimensional (2D) composite model is developed herein that consists of a depth-averaged 2D flow and sediment transport submodel and a bank-erosion submodel. The model incorporates a new technique for updating bank geometry during either degradational or aggradational bed evolution, allowing the two submodels to be closely combined. Using the model, the fluvial processes in the braided reach of the LYR between Huayuankou and Laitongzhai are simulated, and the calculated results generally agree with the field measurements, including the water-surface elevation, variation of water-surface width, and variations of cross-sectional profiles. The calculated average water-surface elevation in the study reach was 0.09 m greater than the observed initial value, and the calculated mean bed elevation for six cross sections was 0.11 m lower than the observed value after 24 days. These errors are attributed to the large variability of flow and sediment transport processes. Sensitivity tests of three groups of parameters are conducted, and these groups of parameters are related to flow and sediment transport, bank erosion, and model application, respectively. Analysis results of parameter sensitivity tests indicate that bank erodibility coefficient and critical shear stress for bank material are sensitive to the simulated bank erosion process. The lateral erosion distance at Huayuankou will increase by 19% as the value of bank erodibility coefficient changes from 0.1 to 0.3, and it will decrease by 57% as the value of critical shear stress for bank increases from 0.6 to 1.2 N/m2. Limited changes of other parameters have relatively small effects on the simulated results for this reach, and the maximum change extent of calculated results is less than 5%. [ABSTRACT FROM AUTHOR]

Alluvial fan evolution and morphology are often considered to respond primarily to external forcing (e.g., tectonics, climate, and base-level change). Here we present a numerical model of alluvial fan evolution that shows that dramatic and persistent fan entrenchment may occur in the absence of such forcing. This process is driven by positive autogenic feed-backs between flow width, sediment transport, and rate of fan aggradation. Entrenchment is initiated where sediment accommodation space limits continued fan growth. Our results highlight a need to rethink both the representation of fluvial width adjustment in landscape evolution models and the established framework for the interpretation of fluvial landforms as archives of environmental change. [ABSTRACT FROM AUTHOR]

Two areas on Mars in the old Thaumasia region were analysed, where interaction between fluvial and tectonic landforms provided conditions to improve age estimation for valley network formation. An Earth analog terrain was also involved in this work at Villány Hills (Hungary) for reference and to see the relations in tectonic-fluvial interaction. On Mars such interaction was observed by morphology (parallel curvatures of neighbour valleys) and by the comparison of statistical analyses of the fluvial and tectonic lineaments' azimuthal orientation. While in the case of Mars the fluvial network elements' distribution closely follows that of the tectonic elements' distribution, in the case of the Earth the connection is weaker. The comparison gives an interesting example for tectonic landforms controlling fluvial valley orientations, occasionally producing resembling features in valley tracks, influencing the sediment transport and the locations of deposits. Because the tectonic faults crossed a much larger area than the fluvial valleys they influenced, crater size frequency distribution based ages could be better measured with them. Using this approach, we found the minimal age of the fluvial network formation to be around 3.7 Ga (or up to 3.9 Ga). This result demonstrates that the small, scattered, and poorly integrated valleys might also have formed at the same period as the larger, branching systems with well determined ages: around the Noachian/Hesperian transition. Thus valley network formation even in the case of small, non-integrated systems might not necessarily extend into the early or middle Noachian ages and might have happened at a potential climatic optimum around 3.7 Ga ago. However the most difficult task remains the exact dating of old and small valleys at other locations on Mars, to confirm this possibility. • Fluvial-tectonic interaction was analysed on Mars and Earth. • Characteristic lineament orientation distribution was found at both sample sites. • Interaction between tectonic faults and fluvial channels were identified on Mars. • Channels followed more accurately the preformed tectonic directions on Mars. • Calculated age for fluvial activity was 3.7 Ga. [ABSTRACT FROM AUTHOR]

Due to the predicted impacts of future climate on hydrology, morphological changes to river channels are expected. Quantifying the magnitudes and rates of future channel change is important for sustainable river channel management. To date, reviews of simulation approaches for investigating river channels and the modelling of environmental change impacts on channel form and process have focused on contemporary process or palaeo perspectives. Hence, herein we review numerical modelling approaches available for reach-scale simulation of future river channels and the predicted in-channel hydro- and morphodynamic changes modelled. We found that despite their widespread availability, hydrodynamic, morphodynamic and cellular models have yet to be used routinely in future in-channel simulations, with cellular models in particular under-represented. Our review shows that predictions of within-channel changes vary greatly between hydro-climatic regions and under contrasting climate change scenarios, mainly due to varying input discharge scenarios; however, increased sediment transport and flood risk are usually predicted. Key challenges in simulating future channel change include representations of external forcing conditions, adequate temporal and spatial scales, transport equations, changing channel materials and lateral erosion; calibration and validation; simulation chains with multiple models; and identification of feedback systems and non-linearity. Nevertheless, despite these challenges, models with increasing complexity have recently been developed and so there is increasing potential in their application. One-dimensional hydro- and morphodynamic simulations, and cellular models, can be modified to reflect the requirements of future representations, such as grain size properties, whilst there is also now an increasing capability to include a greater quantity of external forcing conditions. Some studies, however, have demonstrated the need to develop two-dimensional models for application in centennial-scale studies. We recommend that a wider range of scenarios and the combined effects of multiple external forcing factors should be included, whilst studies are also needed from more hydrologically diverse reaches. [ABSTRACT FROM AUTHOR]

The morphological degradation of fluvial terrace risers provides a constraint to terrace chronology. In this study, we morphologically date the terrace risers along the Kuitun River on the north flank of the Tian Shan, China and subsequently discuss possible relationships between terrace formation and the past regional climate changes and tectonic activity of the Dushanzi fault-related fold. To do this, 159 topographic profile swaths of terrace risers were extracted from LiDAR-derived DEM and were analysed to determine a range of best fitting morphological ages. Through Monte Carlo simulation, a locally applicable sediment transport coefficient (diffusivity) was calibrated as 5.5 ± 1.6 m 2 /ky given the morphological age of the T1/T2 riser and its independently known age. Taking this calibrated coefficient, we estimate age ranges of 11.6 ± 3.4 ka, 6.5 ± 1.4 ka, 5.3 ± 1.1 ka, and 4.2 ± 1.2 ka for terraces T3, T4, T5, and T6, respectively, under the assumption that the age of the riser is close to the abandonment age of the lower surface. These new terrace ages, combining climate proxy records from the oxygen isotope curve from the Guliya ice cap and paleoearthquake events in the Dushanzi fault related fold, suggest that tectonic activity may be an important factor in the formation of lower terraces within the growing anticlines, while in more extensive areas beyond anticlines, climate changes controlled the main deposition and incision events in the present study area, and thus terrace formation of T1–T3. [ABSTRACT FROM AUTHOR]

The interaction between fluvial and aeolian processes can significantly change Earth surface morphology. When rivers and sand dunes meet, the interaction of sediment transport between the two systems can lead to change in either or both systems. However, these two systems are usually studied independently, which leaves many questions unresolved in terms of how they interact. This paper carries out a global inventory, using satellite imagery, to identify 230 sites where there are significant fluvial–aeolian interactions. At each location key attributes such as wind/river direction, net sand transport direction, fluvial–aeolian meeting angle, dune type and river channel pattern were identified and relationships between each factor were analysed. From these data, six different types of interaction were classified that reflect a shift in dominance between the fluvial and aeolian systems. Results from this classification confirm that only certain types of interaction were significant: the meeting angle and dune type, the meeting angle and interaction type and finally the channel pattern and interaction type. However, the findings also indicate the difficulties of classifying dynamic geomorphic systems from snapshot satellite images. [ABSTRACT FROM AUTHOR]

Abstract: Dams are known to create discontinuities in river flow and sediment transport, with ensuing effects on the fluvial geomorphology of dammed systems. While the effects created by large impoundment dams are well documented, less is known about the influence of small run-of-river dams (common across the eastern United States) on river geomorphology. Recent emphasis on dam removal has focused on run-of-river structures, highlighting the need for improved understanding of the geomorphological effects of these types of dams. This research examines spatial variation in channel morphology and bed sediment character upstream and downstream of four run-of-river dams in Illinois. Results show that the four dams do not create major discontinuities in channel morphology or sediment character. Silt/clay content of bed material at the four sites is higher upstream of the dams than downstream, but this size fraction generally is a minor component by weight of the sediment samples collected. Although percentages of sand are generally higher upstream of the dams and gravel percentages are generally higher downstream, not all of these differences are statistically significant. Longitudinal profiles through the dams and changes in channel depth upstream and downstream of the dams indicate that no major accumulations of sediment have occurred behind the dams. Analysis of 137Cs in sediment cores at two sites shows no evidence of long-term fine sediment storage. Apparently, these dams are not acting as major sediment traps, nor do these structures produce substantial downstream channel erosion. Variability in spatial patterns of channel morphology and sediment characteristics among the sites suggests that local site-specific factors have an important influence on geomorphological responses. Because of this variability, the findings of this study indicate that information on site-specific conditions should be an important consideration in the removal planning process for run-of-river dams. [Copyright &y& Elsevier]

We present a 1:33,333 geomorphological map of the Rees Valley, Otago, New Zealand. The Rees River drains an area of ∼405 km2and feeds into the head of Lake Wakatipu. This area has been affected by a range of geomorphological processes including tectonic activity, glacial erosion and deposition, mass movement, fluvial action, and base (lake) level change. Mapping was achieved by a combination of interpretation from SPOT 5 HRG satellite imagery and ground-truthing. The map presents the current distribution of landforms and sediments associated with the wide variety of contemporary and past geomorphological processes. It represents the most detailed and finest resolution geomorphological map of this region to date, and hence a number of features have been mapped and described for the first time. The map will assist on-going studies in the Rees catchment that seek to understand fluvial sediment transport and associated flood hazards, the dynamics of former glaciers, base level change associated with a drop in the level of Lake Wakatipu, and mass movement hazards. [ABSTRACT FROM AUTHOR]

This progress report on the discipline of fluvial geomorphology for the calendar years 2010–2011 extends the analysis carried out by Stott (2010, 2011) of papers published in Earth Surface Processes and Landforms (ESPL) during the calendar years 2006–2007 and 2008–2009 to include the period of 2010–2011. A total of 327 papers were published in the 30 issues of ESPL during the review period, up from 284 during 2006–2007 and 300 in 2008–2009. Of these papers, 175 (54%) were within the subject area of fluvial geomorphology, compared to 125 out of 284 (44%) in the 2006–2007 period, and 113 out of 297 (38%) in the 2008–2009 period. In comparing the three two-year periods covering 2006–2011, the numbers of papers in each of 10 subdisciplines within fluvial geomorphology (e.g. bank erosion, hydraulics, soil erosion) changed markedly. For example, river management, restoration and the effects of vegetation on fluvial systems changed from first in rank in 2006–2007 to tied in fourth place in 2008–2009 and eighth in 2010–2011. In contrast, the subdiscipline of soil erosion was consistently the second-ranked topic in each of the three two-year periods. Following the analysis of patterns of publications in ESPL, selected papers from each of the 10 subdisciplines are reviewed. The articles discussed were selected by searching using keywords from the 10 subdisciplines using http://scholar.google.co.uk, then selecting a relevant journal article from the first 10 hits returned. In this way, 33 papers drawn from 22 journals were sampled and their key findings are summarized. [ABSTRACT FROM AUTHOR]

Invertebrates are important sediment engineers, making up for their small body size with abundance and behavioral diversity. However, despite the recognized importance of invertebrates as sediment engineers in terrestrial and marine environments, zoogeomorphology in rivers has primarily considered larger taxa, such as fish and beaver. This article reviews the zoogeomorphic effects of invertebrates in freshwater habitats, with a focus on rivers. To better synthesize current zoogeomorphic research and to help guide future studies we build a conceptual model considering biotic (behavior, abundance, body size, life history, and species invasions) and abiotic (geophysical energy and sediment grain size) controls on the direction and magnitude of zoogeomorphology. We also incorporate invertebrate engineers into conceptual sediment entrainment models, to understand their geomorphic role in the context of hydraulic power and sediment size. We structure our review around invertebrate behavior as a key control on whether invertebrates have a sediment destabilizing or stabilizing impact. Invertebrate zoogeomorphic behavior are diverse; the majority of research concerns bioturbation, a result of locomotion, foraging, and burrowing behaviors by many taxa. Similarly, burrowing into bedrock by a caddisfly and non‐biting midge larvae promotes bioerosion. Attachment to the substrate, (e.g., silk nets by caddisfly larvae or byssal threads by some mussels) can stabilize sediment, providing bioprotection. Bioconstructions (e.g., caddisfly cases and mussel shells) may have either stabilizing or destabilizing effects depending on their density and abiotic context. Interactions between lotic invertebrates and fluvial processes are complex and understudied, requiring further research across a greater range of taxa, behaviors, and spatiotemporal scales. This article is categorized under:Water and Life > Nature of Freshwater EcosystemsWater and Life > Conservation, Management, and Awareness [ABSTRACT FROM AUTHOR]

The practice of dam removal has received increasing attention as a consequence of maintenance and liability concerns related to the advanced age of many of these structures. Most dams that have been removed thus far are small run-of-river structures. As the number of removals of run-of-river dams increases, it is crucial to understand the effects that these structures have on river geomorphology and sedimentology while in place and how rivers respond to removals so that possible responses to future removals can be anticipated and predicted. This paper reviews current knowledge related to the influence of run-of-river dams on the hydraulics and geomorphology of rivers and suggests types of studies that need to be undertaken to address gaps in current knowledge. Compared to studies of large impoundment dams, field investigations of channel morphology and sedimentology upstream and downstream of run-of-river dams are few and limited in geographic scope. Available studies indicate that the response of rivers to the long-term existence of run-of-river dams is variable both in terms of upstream sediment storage and downstream channel erosion. Future research should focus on how geomorphological responses of rivers to run-of-river dams vary with geographical context and on integration of process-based field studies, numerical modeling and experimental investigations to determine the influence of these dams on flow structure, sediment transport, and patterns of channel erosion and deposition. [ABSTRACT FROM AUTHOR]

Abstract: The fluvial and morphological processes induced by impoundment of the Sanmenxia Reservoir and relevant human activities on the Yellow River and its tributaries are complex. The long‐term annual sediment load of the Yellow River was 1.6 billion tons, ranking first of all the world''s rivers. In 1960, Sanmenxia Dam began filling. Sediment transport in the river then was greatly disturbed and a new cycle of the fluvial processes was induced. First, the dam caused not only anticipated sedimentation in the reservoir, but also serious sedimentation in the largest tributary of the river (the Weihe River). The response of fluvial process to the dam closure varies in space and time. Second, the downstream reaches of the dam experienced erosion and resiltation, changes of river pattern, and development of meanders. Moreover, the downstream reaches of the dam have experienced more and more water diversion, which has induced readjustment of the longitudinal profile of the river. The study reveals that sedimentation in the Sanmenxia Reservoir enhanced the bed elevation at Tongguan, where the Weihe River flows into the Yellow River. The rising Tongguan''s elevation caused retrogressive siltation waves in the Weihe River, which propagated at a speed of about 10 km/yr. An equilibrium sedimentation model is proposed, which agrees well with the data of sedimentation in the Weihe River. In the reaches below the dam the river changes from braided to wandering, or from wandering–braided to wandering–meandering. The discharge released to the downstream reaches has been regulated by the reservoir and it decreases along the course because the quantity of water diversions is more than the inflow from tributaries. The reduction in discharge causes readjustment of the longitudinal bed profile. By using the minimum stream power theory, we prove that the riverbed profile is developing toward an “S‐shape” profile. [Copyright &y& Elsevier]

Reservoirs behind dams act as deposition sites for much of the sediment being transported by rivers. As a result, the downstream river flow can be well below the transport capacity for bed-material. This promotes bed erosion and other geomorphic changes over some length of river located immediately downstream from a dam. These adjustments have been characterized for the Trinity River, TX, downstream of Livingston Dam. Field measurements and results from a 1D numerical model define a 50–60 river kilometer segment of river undergoing bed erosion as the transport capacity for bed material is reestablished. Consequences of this erosion include lowering of the channel bed, reduction in the sediment volume of channel bars, coarsening of sediment on bar tops, steepening of channel banks, and reduction in lateral migration rates of river bends. Repeat surveys of the river long profile reveals that 40 yr of dam closure has produced up to seven meters of channel-bottom incision downstream of the dam, transforming an initially linear profile into a convex-up long profile. The model output matches this observed change, providing confidence that calculated estimates for spatial and temporal changes in bed-material sediment flux can be used to explore the long-term signature of dam influence on the geomorphology of a sand-bed channel. Measurements of channel geometry, profile, lateral migration, and grain size of the lower Trinity River with distance downstream define both the trend and expected variability about the trend associated with the disruption to the bed-material load. [ABSTRACT FROM AUTHOR]

This study describes channel changes following completion of the Provo River Restoration Project (PRRP), the largest stream restoration project in Utah and one of the largest projects in the United States in which a gravel-bed river was fully reconstructed. We summarize project objectives and the design process, and we analyze monitoring data collected during the first 7 years after project completion. Post-project channel adjustment during the study period included two phases: (i) an initial phase of rapid, but small-scale, adjustment during the first years after stream flow was introduced to the newly constructed channel and (ii) a subsequent period of more gradual topographic adjustment and channel migration. Analysis of aerial imagery and ground-survey data demonstrate that the channel has been more dynamic in the downstream 4 km where a local source contributes a significant annual supply of bed material. Here, the channel migrates and exhibits channel adjustments that are more consistent with project objectives. The upstream 12 km of the PRRP are sediment starved, the channel has been laterally stable, and this condition may not be consistent with large-scale project objectives. [ABSTRACT FROM AUTHOR]

The geomorphic evolution of large European fluvial systems since the end of the nineteenth century has been determined, according to recent studies, by changes that have affected the drainage basins, notably climatic changes at the end of the Little Ice Age (LIA), agricultural practices, and successive phases of channel management involving embankments and dams. However, the respective roles of these various control factors in modifying sediment storage and channel stability are often difficult to identify. The aim of this paper is to determine the main factors that have driven morphological changes over the past 130years on the 120-km-long downstream reach of the Rhône River. A GIS-based analysis of maps and aerial photographs available since 1860, coupled with chrono-stratigraphic data on the river's alluvial deposits, has enabled quantification of sediment storage and erosion in different morphological units. Changes measured include riverbed incision, narrowing of the main channel in relation with accumulation of fine sediments along the channel margins, and reduction of sediment input at the mouth. On the basis of local- and reach-scale sediment balances, we show that these changes are synchronous with engineering works carried out at the end of the nineteenth century and beginning of the twentieth century, a period that coincided with a decline in river sediment inputs largely generated by human activities. The early stabilisation of mountain slopes resulting from a decline in rural agriculture, rural exodus, reforestation and engineered torrent control has had a much greater impact in geomorphically transforming the Rhône than dams and gravel mining, the major identified causes of river destabilisation in the world. This calls for caution in the all-too-common and wholesale attribution of declining sediment budgets of European rivers, especially in the Mediterranean region, to dams. [ABSTRACT FROM AUTHOR]

The planform geometry of submarine channels commonly exhibits a spatio-temporal stability generally not observed in fluvial channels. As such, submarine channels tend to lack the meander loop cutoffs and frequent avulsion history typical of fluvial channels. Fluvial sinuosity develops through inner-bend deposition and outer-bend erosion. Inner-bend deposits have also been recognized in submarine channels, from subsurface and seafl oor images and from ancient channel outcrops, and have been demonstrated within physical models. However, outer-bend sediment accumulations are a feature thought to be unique to submarine channels. We report on physical experiments on channelized, subaqueous, particle-driven turbidity currents that demonstrate that channel-fill architecture relates directly to the degree of flow bypass, in turn largely determined by the degree of confinement. In general, weakly bypassing fl ows deposit at the outer bend, whereas strongly bypassing flows deposit at the inner bend. Therefore flows within aggradational channel systems whose axes are bypass dominated may preferentially deposit at the inner bend, ultimately having the effect of increasing channel sinuosity through time; this is an evolution pattern commonly observed in seismic images. Once developed, the apparent spatio-temporal longevity of sinuosity within many systems may be explained by the passage of turbidity currents of varying magnitude (and consequently bypass potential) depositing preferentially at either the inner or outer bank of the channel, maintaining a quasi-stable morphological equilibrium. Fluvial channels do not have the ability to reduce or maintain their sinuosity in this way, which plausibly explains why they tend to develop cutoffs at higher rates than subaqueous channels. [ABSTRACT FROM AUTHOR]

Over the past 10 years the Rosgen classification system and its associated methods of ‘natural channel design’ have become synonymous to some with the term ‘stream restoration’ and the science of fluvial geomorphology. Since the mid 1990s, this classification approach has become widely adopted by governmental agencies, particularly those funding restoration projects. The purposes of this article are to present a critical review, highlight inconsistencies and identify technical problems of Rosgen's ‘natural channel design’ approach to stream restoration. This paper's primary thesis is that alluvial streams are open systems that adjust to altered inputs of energy and materials, and that a form-based system largely ignores this critical component. Problems with the use of the classification are encountered with identifying bankfull dimensions, particularly in incising channels and with the mixing of bed and bank sediment into a single population. Its use for engineering design and restoration may be flawed by ignoring some processes governed by force and resistance, and the imbalance between sediment supply and transporting power in unstable systems. An example of how C5 channels composed of different bank sediments adjust differently and to different equilibrium morphologies in response to an identical disturbance is shown. This contradicts the fundamental underpinning of ‘natural channel design’ and the ‘reference-reach approach.’ The Rosgen classification is probably best applied as a communication tool to describe channel form but, in combination with ‘natural channel design’ techniques, are not diagnostic of how to mitigate channel instability or predict equilibrium morphologies. For this, physically based, mechanistic approaches that rely on quantifying the driving and resisting forces that control active processes and ultimate channel morphology are better suited as the physics of erosion, transport, and deposition are the same regardless of the hydro-physiographic province or stream type because of the uniformity of physical laws. [ABSTRACT FROM AUTHOR]